GtkLabel strong refs the mnemonic widget

[Owen Taylor <otaylor redhat com>]

[ Bug reference: http://bugzilla.gnome.org/show_bug.cgi?id=93334 ]

Another compatibility question. Right now:

 GtkWidget *button = gtk_button_new_with_mnemonic ("_Push Me");
 g_object_ref (button);
 gtk_object_sink (GTK_OBJECT (button);

 gtk_container_add (container, button);
 gtk_container_remove (container, button);

 g_object_unref (button);

Leaks the button and contained label. This is because 
gtk_label_set_mnemonic_widget() makes a strong reference
on the label, so you get a reference loop between the
button and the label.

The obvious fix for this would be to make the reference
a weak reference instead. That, however, is strictly
speaking an incompatible change, because code like:

 GtkLabel *label = gtk_label_new ("Foo');
 GtkWidget *entry = gtk_entry_new ();

 g_object_ref (entry);
 gtk_object_sink (GTK_OBJECT (entry));
 
 gtk_label_set_mnemonic_widget (label, entry);
 g_object_unref (entry);

 [...]

 entry = g_object_ref (gtk_label_get_mnemonic_widget (label));

Woudl no longer work. I think that this is "acceptable breakage - 
I really doubt people use the mnemonic widget property as
the only reference to a widget, but one can always be
suprised...

As always, I'd be interested to here people's opinions on
the matter.

Thanks,
                                        Owen